Robotic systems are used extensively in semiconductor device manufacturing operations in order to minimize operator involvement, optimize efficiency and minimize potential contamination during processing. Robots are commonly employed to transfer one or more semiconductor wafers between storage locations and a plurality of processing stations. For example, a single robot is employed in a so-called “cluster tool” which consists of a modular, multi-chamber, integrated processing system. The robot forms part of a central wafer handling module and functions to transfer the wafers between a number of the peripheral process chambers. The robot is controlled by a controller, such as a PLC (programmable logic controller) which is connected by a multiconductor electrical cable and corresponding connectors to a robotic mechanism. Both the controller and the robotic mechanism have a plurality of electrically interconnected components through which control signals flow for determining the operation of a robot. For example, the controller typically will include a motor controller and a motor drive, and the robot will include multiple motors and corresponding shaft encoders which produce feedback signals indicative of the robot's position. Each of these electrical connecting lines and associated connectors represent opportunities for errors to be introduced into the signals as a result of any of a number of causes, including electrical interference, shorts, open circuits and signal crossover. Even small errors introduced into the control signals by any of these causes can result in robot malfunctions or transfer errors that in turn can produce wafer breakage or even equipment damage. The problem of maintaining signal integrity often becomes more difficult as robots age and the related cabling and connectors begin to experience slight deterioration.
In the past, problems with control signal integrity have been detected only after an error has been introduced into the control signals which has produced a corresponding error in the movement of the robot. Moreover, even after if it is known that there is a problem with signal integrity, it has been very difficult to trace the exact or even general location of the problem.
What is needed is a real-time control signal monitoring system that quickly determines whether an error has been introduced into the control signal and for identifying the location at which the error is introduced. The present invention is directed towards providing this solution.